Cosmos L.T. Guo 1,2, Louis H.S. Lau 1,2, Sunny H. Wong 1,2,3, Raymond S.Y. Tang 1,2, Joseph J.Y. Sung 4

1 Department of Medicine and Therapeutics, Faculty of Medicine, The Chinese University of Hong Kong, 2Institute of Digestive Diseases, The Chinese University of Hong Kong, 3State Key Laboratory of Digestive Disease, Li Ka Shing Institute of Health Sciences, Faculty of Medicine, The Chinese University of Hong Kong, 4Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore

Background/Aims: International guidelines recommend a 10-year surveillance interval in average-risk patients after negative index colonoscopy. Limited evidence is available to support the extension of surveillance interval, particularly in Asia-Pacific region.

Methods: We performed a territory-wide population-based retrospective cohort study involving patients in Hong Kong by the Clinical Data Analysis and Reporting System. All patients who underwent diagnostic colonoscopies with normal findings during 2000-2005 were included, except those with history of colorectal cancer (CRC), inherited CRC syndromes and bowel resection (n = 12,886). All patients were followed longitudinally for interval CRC and death for up to 15 years. Age-standardised incidence and standardised incidence ratios (SIR) were calculated with reference to the general population incidence retrieved from the Hong Kong Cancer Registry.

Results: At baseline, the average age was 55.3±14.7 years, 44.4% of patients were male, 5.5% had diabetes mellitus and 17.0% had history of colonic polyp. Average follow-up time was 13.47±3.54 years. The SIR of CRC at year 5, 10 and 15 were 0.35, 0.26 and 0.39 respectively, indicating a sustained 61% risk reduction in interval CRC for up to 15 years. (Figure 1) Subgroup analysis stratified by age and gender revealed similar findings.

Conclusion: A negative index colonoscopy was associated with 61% reduced risk of interval CRC when compared to general population for up to 15 years. Our findings provide novel data on the potential extension of surveillance interval for CRC among average-risk patients with normal colonoscopy findings.

Keywords: colorectal cancer, interval cancer, negative colonoscopy, surveilance